Such preforms are used in the manufacture of plastic objects in which these objects are manufactured by the molding of preforms. For this purpose, it is necessary to heat the preforms. For example, such devices and methods are used in the manufacture of plastic bottles, which are manufactured by inflating previously heated preforms.
Such devices used for the manufacture of hollow parts such as beverage bottles are sufficiently known from prior art. Thus, for example, WO 0149075 A1 discloses an infrared oven for heating plastic preforms which will later be molded into bottles. In the process, preforms are passed by infrared radiators, and are heated by them. Because very many plastics (e.g., PET) have the property that the external surface gets hot more quickly than the internal surface, it is necessary to ensure temperature equalization during the heating process. As a result, it is necessary to expose the preform to cooling air during the heating process so that the external surface of the preform does not get too hot during the heating process, which would cause crystallization at the surface, rendering the preform unusable. It is further necessary to cool the neck finish of the preform because it must be heated only very little in order later to achieve correct seating of the closure on the neck finish.
WO 0149075 A1 thus discloses a fan through which cooling air is conveyed in the direction of the preform and the infrared lamps. Furthermore, the same cooling air is used to cool the area of the neck finish of the preform.
This device has the disadvantage that cooling of the area of neck finish of the preform cannot be precisely adjusted because it is dependent on the adjusted volumetric flow rate or mass flow rate of the cooling air for the body area of the preform. Because cooling of the surface of the body area of the preform takes priority, adjustment of the volumetric flow rate of the cooling air conforms to the optimal parameters for cooling the body. It may therefore occur that the neck finish is cooled too little, which would lead to unusability of the preform, or that the area of neck finish is cooled too much, which would lead to excessive use of air by the device, which constitutes uneconomical operation of the system.